PEF2091 Siemens Semiconductor Group, PEF2091 Datasheet - Page 188

• Manufacturer Part Number: PEF2091
• Description: ICs for Communications(ISDN Echocancellation Circuit)
• Manufacturer: Siemens Semiconductor Group

Semiconductor Group
Analog Loop-Back Control
Before an analog loop-back is closed with the C/I-command ARL (activation request
loop-back, see "C/I Channel Codes", page 224), the device should have been reset.
In order to open an analog loop-back correctly, reset the device into the TEST state with
the C/I-command RES (or by pin reset). This ensures that the echo coefficients and
equalizer coefficients will converge correctly when activating the following time.
Although loop-back #1 and loop-back #3 are closed with the same command and
perform the same function, they cannot be started from the same state: Loop-back #1 is
closed when in the state "Deactivated" (LT side); loop-back #3 can only be closed in the
state "Test" (NT side).
For examples of programming these loops, refer to "Examples for Analog Loop-Back
Control", page 236.
4.7.2
For loop-back #2 several alternatives exist. Both the type of loop-back and the location
may vary. Three loop-back types belong to the loop-back-#2 category:
– Complete loop-back
– B1-channel loop-back
– B2-channel loop-back
The complete loop-back comprises both B-channels and the D-channel. It may be closed
either in the IEC-Q itself or in a downstream device. Single-channel loop-backs are
always performed within the IEC-Q. In this case the digital data of DOUT will be directly
fed back into DIN. This also applies if the complete loop-back is closed in the IEC-Q.
Normally loop-back #2 is controlled from the exchange. The EOC commands LBBD, LB1
and LB2 are used. They will be recognized and executed automatically in the NT IEC-Q
if the EOC Auto mode is selected (see "EOC Auto/Transparent Mode", page 55). Due to
the automatic acknowledgment in EOC Auto mode, the EOC-message will be mirrored
back immediately by the NT as a confirmation
MON-0 messages. For more details, see "Access to EOC of U-Interface", page 110.
If the EOC Transparent mode is used in the NT the MON-8-commands LBBD, LB1 and
LB2 are available (see "EOC Auto/Transparent Mode", page 55).
All loop-back functions are latched. This allows channel B1 and channel B2 to be looped
back simultaneously. All loop-backs are opened when the EOC command RTN or the
MON-8 command NORM is sent.
A detailed operational description will be give in the subsequent sections.
1) Note however that this confirmation is issued before the loop-back function is initialized.
Therefore it cannot be regarded as an acknowledgment that the loop-back function was started
correctly
Partial and Complete Loop-Back (No. 2)
188
1)
. EOC commands are accessed via
Operational Description
Data Sheet 01.99
PEB 2091
PEF 2091